Heat resistant alloy steel

ABSTRACT

A heat-resistant alloy steel composed of 0.05 to 0.40 percent by weight of carbon, 0.5 to 1.0 percent by weight of silicon, 0.2 to 1.0 percent by weight of manganese, 20.0 to 23.0 percent by weight of chromium, 0.5 to 2.5 percent by weight of molybdenum, 0.5 to 3.5 percent by weight of tungsten, 0.5 to 3.5 percent by weight of niobium, and the balance iron and unavoidable impurities, the tantalum content in the niobium being not more than about 10 percent by weight.

ilnited States Patent Inventor Hidcki Terada Aid-gun, Horoshima-ken,Japan Appl. No. 676,172 Filed Oct. 18, 1967 Patented Nov. 2, 1971Assignee Toyo Kogyo Company Limited Aid-gun, Hiroshima-ken, JapanPriority Oct. 21, 1966 Japan 41/69550 HEAT RESlSTANT ALLOY STEEL 1Claim, 2 Drawing Figs.

10.8. C1 75/126 C, 75/126 F Int. Cl C22c 39/20 Field 01 Search 75/126 C,126 F, 126

Reierences Cited UNITED STATES PATENTS Becket 1-1siao Kirkby Binder...

Giles Harris Primary Examiner-Hyland Bizot Attorney-Wender0th, Lind &Ponack 75/126 75/126 F 75/126C 75/126C 75/126 F ABSTRACT: Aheat-resistant alloy steel composed of 0.05 to 0.40 percent by weightofcarbon, 0.5 to 1.0 percent by weight of silicon, 0.2 to 1.0 percent byweight of manganese, 20.0 to 23.0 percent by weight of chromium, 0.5 to2.5 percent by weight of molybdenum, 0.5 to 3.5 percent by weight oftungsten, 0.5 to 3.5 percent by weight of niobium, and the balance ironand unavoidable impurities, the tantalum content in the niobium beingnot more than about 10 percent by weight.

HEAT RESISTANT ALLOY STEEL The present invention relates to aheat-resistant alloy steel. It also relates to a heat-resistant ferriticalloy steel which is excellent in resistance to corrosion, deformationand cracking under high temperature and corrosive environments. Itfurther relates to an insert for the precombustion chamber of a Dieselengine which is made of the said alloy steel.

For such purposes as mentioned above, there have been used (I) NimocastPE-lO (2) a nickel-based ultra-heat-resistant alloy steel, (3)lnconel-6l0, (4) a highly carburized heat-resistant austenitic alloysteel, (5) a heat-resistant austenitic alloy steel, and (6) aheat-resistant ZI-chromium" ferritic alloy steel. However, these are notsatisfactory in deformation and crack resistant properties. Further,they are disadvantageous in that they are expensive owing to the largecontent of such costly elements as nickel, niobium tungsten, molybdenumand the like.

Accordingly, a fundamental object of the present invention is to providea new heat-resistant alloy steel. Another object of this invention is toprovide a new formulation ofa ferritic alloy steel. A further object ofthe invention is to provide a steel which is deformation and crackresistant at an elevated temperature. A still further object of theinvention is to provide an insert for the precombustion chamber of aDiesel engine which is made of the heat-resistant alloy steel. These andother objects will be apparent to those conversant with the art to whichthe present invention pertains from the foregoing and subsequentdescriptions, taken with the accompanying drawing, in which:

FIG. l is a plan view of a precombustion chamber insert; and

FIG. 2 is a section on line 2-2 of FIG. 1.

The alloy steel of the present invention is composed of 0.05

to 0.40 percent by weight of carbon, 0.5 to l.0 percent by weight ofsilicon, 0.2 to 1.0 percent by weight of manganese, 20.0 to 23.0 percentby weight of chromium, 0.5 to 2.5 percent by weight ofmolybdenum, 0.5 to3.5 percent by weight of tungsten, 0.5 to 3.5 percent by weight ofniobium, and the balance iron and unavoidable impurities, the tantalumcontent in the niobium being not more than about 10 percent by weight.

In the alloy steel of the present invention, an excess amount of carbonresults in deficiencies owing to the formation of carbides of chromium,molybdenum, tungsten and the like. Further, it decreases the solidsolubilities of those metals in TABLE 1 weight does not affect thecrack-stopping property, because the alloy is constituted by a soleferrite form. But, the upper limit ofthe chromium content is to be atthe most 23.0 percent by weight, because of the cost and the balancebetween the austenite and the ferrite forms under a carburizingcondition.

Molybdenum and tungsten are each required for the deformationresistance, and the content should not be less than 0.5 percent byweight. Since excess amounts of them affect unfavorably thecrack-resistance, the molybdenum and tungsten contents should berestricted to at the most 2.5 percent by weight and 3.5 percent byweight, respectively.

Niobium provides crack-resistance and gives a fine-grained steel. Thiseffect is attributed not to niobium per se, but to niobium carbide.According to the experiments, a combination of l percent by weight ofniobium and 0.1 percent by weight of carbon or of 3 percent by weight ofniobium and 0.3 percent by weight of carbon produces the most excellenteffect on the fineness of the grain. Thus, with a content of 0.05 to0.40 percent by weight of carbon more than 3.5 percent by weight ofniobium results in high cost instead of increasing crack-resistance, anda fine-grained steel can not be formed with a content less than 0.5percent by weight ofniobium, that is to say the niobium content has tobe within the range to 0.5 to 3.5 percent by weight. It should be notedthat less than about 10 percent by weight of tantalum may be containedin the said niobium. It is confirmed by the experiments to determine theeffects of each carbon and niobium per se that when carbon was increasedto 0.4 percent from 0.04 percent and niobium by weight and was increasedto 30 percent from 0.5 percent respectively, the absolute heatdeformation value was increased by 33p.(corresponding to the carbonincrement) and 30 (corresponding to the niobium increment), respectivelyand the number of cycles before the occurrence of cracks was alsoincreased by 20.0 (corresponding to the carbon increment) and 12.0(corresponding to the niobium increment).

Silicon and manganese are added as the deoxidation agents. Tl-iedeoxidation can be sufficiently achieved with 0.5 to L0 percent byweight of silicon and 0.2 to L0 percent by weight of manganese withoutany decrease of the strength of the objective alloy steel.

Using the thus-composed alloy steel, an insert for the precombustionchamber of the Diesel engine as shown in FIGS. 1 and 2 is cast by aconventional method, e.g. a lostwax process.

To examine the crack and a deformation resistances of the alloy steel ofthe present invention, the test pieces in the form Composition (percentby Weight) NOTE.NOS. 1 to 6 are the previously known compositions andNos. 7 to 10 are the compositions of the present invention.

the alloy base, and also prevents the dispersion of nitrogen during aTufftride process (i.e. soft-nitriding process) to make thin the layerof the mixture of iron carbide and iron nitride. Taking these facts intoconsideration, it has been decided that the upper limit of the carboncontent should be 0.40 percent by weight. It is necessary for goodstrength of the alloy steel that the carbon content should not be lessthan 0.05 percent by weight.

At least 20.0 percent by weight of chromium is required to make thealloy steel corrosion and crack resistant, especially under an oxidativeenvironment at an elevated temperature.

An increased chromium content more than 20.0 percent by of the abovementioned insert were cast in six kinds of known alloy steels and fourkinds of the present alloy steels, having compositions shown in Table 1.

Three pieces were cast in each of ten compositions; and directlysubjected to the testing and another three pieces of all but the fifthcomposition, a heat-resistant austenitic alloy steel, were cast andsubjected after heat treatment or a surface treatment by the Tufftrideprocess. ln the heat treatment, the formation of solid solution wasexecuted at l,l00 C. for 2 hours and the crystallization ofthe alloy at750 C. for 2 hours. The Tufftride surface treatment was carried out at560 C. for 2 hours.

The test was carried out by heating each of the 57 test piecesintermittently and repeatedly so that they were treated substantiallyunder the same condition as in the engine. That is, each test piece wasplaced in a metal holder which was cooled by running water. Anyoxygen-acetylene burner was provided to heat the upper surface of thetest piece. A rotating cam was used to successively move the nozzle ofthe burner forwards to direct the flame onto the test piece at an angleof 65 for 24 seconds (whereby the temperature of the reverse side of thepiece was elevated to 1.0l-l,045 C. and rearwards, away from the testpiece for 30 seconds (whereby the temperature of the reverse side waslowered to 350-3 60 C.),

and the cycle was repeated 500 times.

Deformation values for each set of three test pieces were measuredduring each cycle, along equiangularly spaced axes X-X, Y-Y, N-N and 5-8(shown in FIG. 1) in the region A-A (shown in FIG. 2), and along axesX-X, N-N and S- S in the region B-B (FIG. 2). In the table 2, under theheading Deformation values the averages of the deformation values in theregions A-A, 8-8 are listed in appropriately marked column. The averagesin the A-A column are found by adding the deformation values along the 4axes for each of the 3 test pieces and then dividing by 12. The averagesin the 8-8 columns are found by adding the deformation values along the3 axes for each of the 3 test pieces and then dividing by 9. The valueslisted in the columns marked Average" are found by multiplying theappropriate A-A and B-B averages respectively by 4 and 3, adding theproducts and then dividing by 7.

Columns marked A-A," B-B and Average" are provided under subheadingSubtractive values" and Absolute values." The averages listed under thefirst of these subheadings are found by qualitative addition of thedeformation values, that is to say, by adding expansions and subtractingcontractions. The averages listed under the second of these subheadingsare found by "qualitative" addition of the deformation values, that isto say. by adding the amounts of deformation without regard to thenature of the deformation as expansions or contractions.

THe average number of cycles taken before cracking took place were alsodetermined and noted in Table 2.

From the results in listed in Table 2, it is apparent that the alloysteels Nos. 7 to 10 of the present invention are significantly superiorto those Nos. 2 to 6 of the previously known compositions in combinedcrack and deformation resistant properties when merely cast. It is alsonoted that the deform ation-resistance of the alloy steels according tothe invention is remarkably improved by the surface treatment, althoughthe crack-stopping property is affected somewhat unfavorably.Heat-resistant alloy steels of the present invention are alsoeconomical, because the amounts of expensive metal are decreased, andare therefore superior to the known alloy steels such as Nimocase P510in general engineering properties.

The test results of Table 2 can be confirmed by the continuous workingtrials for 1000 hours. where the insert made of the present alloy steelis actually assembled in the Diesel engine.

As disclosed above, there is provided a heat-resistant t'erritic alloysteel which is deformation and crack-resistant at elevated temperatures,and this material is especially suitable for use in the precombustionchamber of 21 Diesel engine.

What is claimed is:

1. A heat-resistant alloy steel the provision "for use as an insert in adiesel engine combustion chamber" consisting essentially of 0.05 to 0.40percent by weight of carbon, 0.5 to l.0 percent by weight of silicon,0.2 to 1.0 percent by weight of manganese, 20.0 to 23.0 percent byweight of chromium. 0.5 to 2.5 percent by weight of molybdenum. 0.5 to3.5 percent by weight of tungsten, 0.5 to 3.5 by weight of a materialwhich is at least 90 percent by weight-pure niobium and the resttantalum, and the balance iron and unavoidable impurities.

TABLE 2 Deformation values (a) Cycle Subtractivc values Absolute vnlnvsN05. to

(311115! Number AA Illl Avi-rngv A- A B l! AVI'IZIKU crackingPreparation The known compositions:

l I 40 t4 58 H0 101 .13 158 asting.

1 -15 7 -12 73 53 (15 .23 Ill-at trt-ntmcnt. l -197 327 253 107 327 .253I30 Casting. l 156 2l5 181 156 .215 181 88 Surface trcatnn nl. 3 t 1S0423 284 180 423 284 170 Casting.

l 287 -60? 425 1181) 607 425 I03 Heat treatment. 4 l30 68 103 I61 05 13340 Casting.

Q -93 -42 -71 135 75 109 :8 Surface treatment. 5.. -18I 445 294 181 445294 1204 Casting. I75 497 -3I3 185 497 31!) I Casting.

l 107 327 201 107 327 .301 I23 Surfacctrcatmt'llt. The compositions ofthe invention:

.. 1 -55! 265 148 84 265 100 370 Casting. e r r r r r 1 -48 -79 -61 84til 87 J6 Surface treatment. 8 i 7.) 134 -103 82 134 I05 140 Casting.

r r r r -8 -15 -11 3.) 57 Surface treatment. 0 -52 89 G7 77 8'.) 175Casting. -9 7 3 (14 34 51 50 surface treatment. 10 l 73 -16U 90 167 123200 Casting.

-- '1 -25 35 -30 83 5t) 72 50 Surface treatment.

Note: Casting refers to casting without lleatand surface-treatments.Heat treatment refers to soaking in air at 1100 C. for 2 hours and at750 C. for 2 hours. Surface treatment" refers to "Tufftriding" at 560 C.for 2 hours.

